Increasing the performance of general-purpose computer systems, while lowering the cost to produce such systems, is a major challenge to computer designers and manufacturers. In fact, the price/performance ratio of a particular computer may be the decisive factor in the sale of that system. As a result, much time and money has been spent improving the technologies used to develop various digital logic integrated circuit chips used in these computers.
Complementary metal-oxide semiconductor (CMOS) logic is known for its relatively high transistor packing density. It is therefore a very popular choice for use by integrated circuit chip designers to improve the performance of their computers in, for example, the design of microprocessors. However, improvements in the CMOS fabrication process, resulting in hundreds of thousands of transistors disposed on a chip, cost millions of dollars in development expenditures. In addition, these VLSI chips generate large amounts of heat energy which must be dissipated. Emitter-coupled logic (ECL), on the other hand, is known for being one of the fastest logic families in terms of transistor switching characteristics. Yet, its power dissipation ranks among the highest of all the logic families.
Most modern CMOS chips used in general-purpose computer systems are designed to operate in 40.degree. C. ambient temperature. When the ambient temperature increases, the operating temperature of the transistors contained within the chips increases beyond the design specification, causing thermal and chemical breakdown of the devices. Conversely, as the ambient temperature decreases within a predetermined range, the speed of the chips increases linearly. Also, the reliability of the chips increases approximately exponentially with a decrease in temperature.
Prior attempts to increase the performance of chips include utilizing liquid nitrogen cooling, conventional air cooling with heat sinks, and refrigeration. One of the more effective approaches in terms of price/performance ratio involves the use of a refrigeration system to cool an entire computer cabinet. The use of known refrigeration technology to lower the operating temperature within a cabinet can result in a substantial increase in the speed of a computer for a modest price increment, but there are reliability problems associated with this cooling technique. Since the temperature inside the cabinet is often below freezing, frosting occurs when the computer cabinet is opened for maintenance or reconfiguration of the system, creating water which could damage the electronics contained within the computer.
The insertion of CMOS chips into liquid nitrogen has approximately doubled the speed of the chips. Cryogenically cooled CMOS supercomputers, which claim a 160% speed improvement over conventional air-cooled computer systems, are commercially available. However, the liquid nitrogen cost structure is twice that of conventional air-cooling. The development and physical size of the liquid nitrogen engine and insulated flask are cost factors, as are the staff and power sources required to support such equipment. The reliability of the apparatus is also a 0 concern. Since liquid nitrogen cooling involves both mechanical and electrical interconnection of various components, the mean time between failure of the nitrogen engine and related parts is substantially lower than that of conventional air-cooling techniques.
An attempt has been made to utilize a Peltier device as a means for controlling the temperature of a bubble memory within a narrow temperature band. One arrangement is shown in U.S. Pat. No. 4,685,081 issued to Richman on Aug. 4, 1987, entitled "Peltier Junction Used For Thermal Control Of Solid State Devices."
In an alternate method for cooling in a computer environment, a computer cabinet will include a fan which provides air-cooling, the fan being located at a position for directing air over and through the circuit boards with appropriate ventilation being provided in the cabinet. However, the heat energy dissipated by a VLSI chip is too great for sufficient cooling by direct air thermal transfer.
Therefore, a problem encountered with computer systems is cooling or lowering the ambient temperature in which the computer system, or more specifically the individual integrated circuit chips, operate in order to improve the overall performance of the computer.
Also, a problem facing computer designers concerns increasing the speed and reliability of CMOS integrated circuits in an economical manner, such that the chips exhibit the speed associated with ECL logic, while retaining the high transistor packing density characteristic of CMOS logic.